There have been investigations into the incorporation of thermally conductive filler into the curable epoxy resin compositions used as sealants and adhesives for electrical/electronic components and into the utilization of the resulting compositions as adhesives for bonding a heat source, such as a semiconductor chip, to a heat sink member. The cured products from such compositions, however, have had a high modulus and have been stiff, which has quite readily resulted in the generation of large stresses on the electrical/electronic component, such as a semiconductor chip, due to thermal expansion of the cured material. This has resulted in problems such as warping of the electrical/electronic component or substrate, the appearance of cracks in the cured product itself, the generation of gaps between the electrical/electronic component and the cured product, and even in failure of the electrical/electronic component. Moreover, while this cured product needs to be flame retardant, the flame retardancy has been inadequate.
In order to reduce the stress associated with the cured product, die-attach pastes comprising epoxy resin and the reaction product of cyanate resin with an epoxy-functional dimethylsiloxane compound (refer to Japanese Laid-Open (Unexamined) Patent Application Numbers Hei 10-147764 (147,764/1998) and Hei 10-163232 (163,232/1998)) and die-bonding agents comprising the reaction product of epoxy-functional silicone oil and a phenolic organic compound (refer to Japanese Laid-Open (Unexamined) Patent Application Numbers Hei 7-22441 (22,441/1995), Hei 7-118365 (118,365/1995), and Hei 10-130465 (130,465/1998)) have been introduced. However, the cured products afforded by these materials are still stiff and the stress-reducing effect is inadequate.
In another vein, curable silicone compositions provide cured products that have excellent electrical characteristics, e.g., dielectric characteristics, volumetric resistivity, and dielectric breakdown strength, and for this reason are used as sealants and adhesives for electrical/electronic components. However, they yield cured products that are, conversely, soft and that have a low mechanical strength and a low modulus, and this has resulted in a poor capacity to protect electrical/electronic components, that is, a poor performance with regard to protecting electrical/electronic components from external impact or shock. In addition, these cured products, because they exhibit low adhesiveness for electrical/electronic components, have been associated with the facile generation of gaps between the cured product and these components. While there have been attempts at improving the modulus and mechanical strength of the cured product by incorporating filler into the curable silicone composition, this results in a loss of the softness and flexibility. The generation of thermal conductivity through the incorporation of metal powder (e.g., silver, copper, and so forth) into curable silicone compositions has been studied, but this approach results in a low flame retardancy by the cured material thereby afforded.
Japanese Laid-Open (Unexamined) Patent Application Number Hei 6-306084 (306,084/1994) discloses a curable silicone composition that has a short gelation time; this curable silicone composition comprises epoxy-modified silicone oil and phenol-modified silicone oil. This curable silicone composition, however, exhibits a poor curability and requires a lengthy period of heating for cure. In addition, it generates a very brittle cured product.
It is an object of the present invention to provide a curable silicone composition that has excellent handling characteristics and that cures rapidly to give a cured product that is highly thermally conductive, very flexible, highly adhesive, and very flame retardant. It is a further object of the present invention is to provide a cured product that is highly thermally conductive, very flexible, and very flame retardant.